Stable Blue Phosphorescent OLEDs Based on a Tetradentate Pt(II) Complex with Extended π-Conjugation.

Achieving simultaneously high efficiency and long operational lifetime in blue organic light-emitting diodes (OLEDs) remains a major challenge. Herein, we report a newly designed blue tetradentate Pt(II) complex, PtTP, featuring a biphenyl substituent on the benzocarbene moiety to extend π-conjugation and steric tert-butyl groups to suppress aggregation, together with weak intramolecular noncovalent interactions. As a result, PtTP exhibits a high photoluminescence (PL) quantum yield of 97% in a 5 wt % poly(methyl methacrylate) (PMMA)-doped film and excellent thermal stability (Td = 500 °C). The device based on PtTP exhibits efficient blue phosphorescence with an external quantum efficiency (EQE) of 23.3% at 100 cd/m2 and maintains an EQE of 17.5% even at an ultrahigh luminance of 10,000 cd/m2, indicating remarkably small efficiency roll-off. Moreover, the device achieved significantly improved operational stability, with an LT50 of 378 h at an initial luminance of 1000 cd/m2. These results demonstrate that synergistic π-conjugation extension and steric engineering provide an effective strategy for realizing highly efficient and stable blue OLEDs.